In the United States, mobile wireless appliance locating equipment is being deployed for the purpose of locating wireless callers who dial 911. Other services in addition to emergency call servicing are contemplated and are referred to as location based services (LBS). Wireless location equipment is typical employed as a overlay to wireless communication networks, thus forming a network overlay geo-location system.
In operation, these network overlay location systems take measurements on RF transmissions from mobile appliances at base station locations surrounding the mobile appliance, and estimate the location of the mobile appliance with respect to the base stations. Because the geographic location of the base stations is known, the determination of the location of the mobile appliance with respect to the base station permits the geographic location of the mobile appliance to be determined. The RF measurements of the transmitted signal at the base stations can include the time of arrival, the angle of arrival, the signal power, or the unique/repeatable radio propagation path (radio fingerprinting) derivable features. In addition, the geo-location systems can also use collateral information, e.g., information other than that derived for the RF measurement to assist in the geo-location of the mobile appliance, i.e., location of roads, dead-reckoning, topography, map matching etc.
Angle of arrival (AOA) is a well-known measurement that can be made on an RF signal for the purpose of locating a mobile appliance operating in a wireless communications network. There have been many methods disclosed to produce the AOA. Many of these methods use some method of calibration to take into account the dynamic nature of the components in path prior to the signal measurements made to estimate AOA. In general, the calibration is composed of coupling or injecting a known signal simultaneously into the receive signal paths at or close to the antenna array, and measuring the inter-channel characteristics of the test signal to characterize the traversed components (antenna beam formers, cables, RF distribution units, filters, etc.).
However these methods do not specifically deal with the problems that arise when the mobile appliance is operating in a wireless network that utilizes frequency hopping, such as the GSM air interface. The use of frequency hopping in wireless air interfaces is well known, and exemplified by GSM, the most widely deployed air interface in the world, therefore there is a need to address the problems confronted when locating frequency hopping mobile appliances.
The current subject matter provides novel approaches for efficiently calibrating an antenna and signal processing equipment, to allow generating accurate AOA measurements in equipment intended to locate wireless mobile appliances operating in a network employing frequency hopping. The novel approaches includes calibration methodologies and configurations.
In order to obviate the deficiencies of the prior art, it is an object of the current subject matter to present, in a network overlay geolocation system, a novel improvement in a method for locating a mobile appliance. The method including determining the AOA of an uplink signal from the mobile appliance at a base station from measurements, by a wireless location sensor, of an attribute of the uplink signal and a frequency specific calibration of a path between a multi element antenna array and the wireless location sensor. The novel improvement, wherein the uplink signal is a frequency hopping signal and including collecting segments of a frequency hopping signal associated with each hop and calibrating the path, at approximately the respective segment's hop frequency and proximate in time to collecting the respective segments. The improvement also including, estimating the AOA of a frequency hopping signal from the collected segments and the path calibrations.
It is also an object of the present subject matter to present, in a network overlay geolocation system, an improvement to a method for locating a mobile appliance. The method including determining the AOA of an uplink signal from the mobile appliance at a base station from measurements, by a wireless location sensor, of an attribute of the uplink signal and a frequency specific calibration of a path between a multi element antenna array and the wireless location sensor. The novel improvement, wherein the uplink signal is a frequency hopping signal and further includes collecting segments of a frequency hopping signal associated with a specific hop; calibrating the path, at approximately the specific hop's frequency, proximate in time to the collecting of each segment, over a plurality of hopping sequence cycles. The improvement also including estimating the AOA of a frequency hopping signal from the collected segments associated with the specific hop and the path calibrations at approximately the specific hop's frequency.
It is still a object of the current subject matter to present, in a network overlay geolocation system, an improvement to a method for locating a mobile appliance. The method including determining the AOA of an uplink signal from the mobile appliance at a base station from measurements, by a wireless location sensor, of an attribute of the uplink signal and a frequency specific calibration of a path between a multi element antenna array and the wireless location sensor. The novel improvement, wherein the uplink signal is a frequency hopping signal and further includes collecting segments of a frequency hopping signal associated with each frequency hop; calibrating the path, at a predetermined frequency and proximate in time to the collecting of each of the segments. The improvement also including estimating the AOA of a frequency hopping signal from the collected segments and the path calibrations at the predetermined frequency.
It is an additional object of the current subject matter to present, in a network overlay geolocation system, a novel improvement to a method for locating a mobile appliance. The method including determining the AOA of an uplink signal from the mobile appliance at a base station from measurements, by a wireless location sensor, of an attribute of the uplink signal and a frequency specific calibration of a path between a multi element antenna array and the wireless location sensor. The novel improvement, wherein the uplink signal is a frequency hopping signal and further includes collecting calibration data for each of the hop frequencies in the frequency hopping sequence; determining a relationship between the calibration data at a selected hop frequency and the other hop frequencies; collecting segments of a frequency hopping signal associated with each hop; calibrating the path, at the selected hop frequency and proximate in time to collecting the segment associated with each hop. The improvement further including estimating the AOA of a frequency hopping signal from the collected segments, the path calibrations at the selected hop frequency and the determined relationship between the calibration data for the selected hop frequency and the respective hop's frequency.
It is another object of the present subject matter to disclose a novel method of calibrating an antenna array and signal processing for receiving a frequency hopping communication signal. The method including the steps of obtaining frequency hopping operational information of the signal, receiving the signal, and injecting calibration signals at frequencies of the frequency hopping sequence in response to receipt of the communication signal. The method further including determining calibration coefficients C1 and C2 for said at least two frequencies and applying C1 and C2 to calibrate the antenna and signal processing equipment to a received signal.
It is still another object of the present subject matter to disclose a novel method of calibrating an antenna array and signal processing for receiving a frequency hopping communication signal. The method including obtaining frequency hopping operation information of the signal and receiving the signal. The method injecting a calibration signal at one frequency of the frequency hopping sequence of the signal in response to receipt of the signal and determining a calibration coefficient C1 for the one frequency and, applying C1 to a received signal at each frequency in the received signal to calibrate the antenna and signal processing equipment.
It is yet another object of the present subject matter to disclose a novel method of determining an angle of arrival of a frequency hopping communication signal. The method including obtaining frequency hopping operation information of the signal and receiving the signal over multiple hops of the same frequency. The method including injecting a calibration signal at one frequency of the frequency hopping sequence of the signal in response to receipt of signal and determining a calibration coefficient C1 for said one frequency. The method further includes determining the AOA of the signal based on the hops of the signal having said one frequency and the calibration coefficient C1.
It is still yet another object of the present subject matter to disclose a novel method of calibrating an antenna array and signal processing for receiving a frequency hopping communication signal. The method including periodically injecting calibration signals at frequencies in the frequency band of the system and determining and storing calibration coefficients for the frequencies. The method then determines relationships relating calibration coefficient of one frequency to the calibration coefficients of each of the other frequencies using the stored calibration coefficients. The method involves obtaining the frequency hopping operational information of the signal and receiving said signal. The method further includes injecting a calibration signal at one frequency in response to receipt of said signal and determining a calibration coefficient C1 for said one frequency and, determining calibration coefficients for said other frequencies based on the calibration coefficient for said one frequency and the determined relationships. The method includes applying the calibration coefficients corresponding to the frequencies of the received signal to the received signal.
These objects and other advantages of the disclosed subject matter will be readily apparent to one skilled in the art to which the disclosure pertains from a perusal or the claims, the appended drawings, and the following detailed description of the preferred embodiments.